When an 18-year-old musician struck up an online friendship with Carly Ryan, 15, in 2007, chat rooms and social media were in their infancy.

Online predators were not spoken about, 'catfishing' was not yet a term and for this South Australian teenager, her trust in the boy she'd been chatting to for 18 months led her into the deadly hands of a murderer.

For mother Sonya Ryan, she saw her grief as a choice.

"All of a sudden my daughter was killed by an online predator and it completely annihilated my world," Ryan told The Huffington Post Australia.

"I was left with choice -- to just dissolve, it’s over, or you fight.

"I have made that choice to fight and to do what I feel my daughter would have wanted, to prevent crimes and to find ways to keep people safe.

"She was a really compassionate kid and I feel this is what she would have wanted me to do."

Named Thread, the app is a way of discretely checking in with friends and family at the touch of a button, to say you've arrived home safely, or that you made it to sports practice. You can also send a map of where you are or a photo.

Thread also has an alert function, which immediately calls 000 and alerts your chosen contacts, sending your location, or a photo with a photo and your location.

"It's not something that tracks teenagers all the time -- it's something they have to want to use," Ryan said.

"It's using technology to easily connect with the people who love and care about it."

It's free for Android and iPhone and was created by created by digital specialists KOJO with some funding from the South Australian Government.